Re: OT: servers vs. lightning and power outages

[Stan Hoeppner <stan@hardwarefreak.com>]

Jerome BENOIT put forth on 3/14/2011 7:58 PM:

> Just curious:
> why the UPS must be at the bottom ?

Your attempt at being a smart ass aside, I'll answer your question.  The
answer, however, isn't the simple one you're expecting.

I stated bottom of the server rack explicitly because some SAs install
all of their UPS gear in a single dedicated rack, or two, or xx, and
feed PDUs in their server racks, often ignorantly over loading their UPS
output circuits in the process.  And yes, these SAs will load a 42U rack
bottom to top with UPS units.  I had to do this on one occasion myself
due to an ill conceived pre-existing equipment layout.  Thankfully the 4
Liebert 3000s I had to mount in the top of the UPS rack only weighed
about 80 lbs apiece.  The first one was tough, but the last 3 were
relatively easy.  Ego boost prize goes to the first OP to reply
correctly explaining why this was the case.

Unrelated to that incident, I prefer to install one properly sized UPS
(and battery packs if needed) in the bottom of each server rack.  There
are a few benefits to doing this:

1.  Cleaner cabling, less radiated EMI/RFI
2.  Shorter cable runs means less resistance, thus
    lowering the impedance load on the UPS, yielding slightly higher
    overall efficiency.
3.  The immense mass usually lowers the rack center of gravity
    sufficiently to eliminate the need to bolt the rack to the floor,
    while still allowing you to slide servers out for maintenance
    without tipping the rack over on yourself

-- 
Stan